The present invention relates to a thermal printer and a thermal printing method.
Conventionally, thermal printers of the high density type and high speed type are known. A print head of such a thermal printer of this high density type has a plurality of heating elements each of which has a printing surface of small area and which are arranged in a line with a narrow dot distance. The head is driven step by step in a direction of the printing line in the short cycle corresponding to the narrow dot distance in the printing operation, and the current pulses are supplied to the selected heating elements in accordance with the data to be printed, thereby printing the dot pattern with high density on a thermal recording paper or on a recording paper through the ribbon on which a thermally melting ink was coated, However, in this case, it is required to execute a number of printing cycles to print the dot data of one line, so that the print speed will become slow. Furthermore, in the high speed thermal printer, the printing surface of each heating element has a larger area than that of the thermal printer of the high density type and the heating elements are arranged with a larger dot distance. In the printing operation, the head is step-driven in the cycle corresponding to the large dot distance, and at the same time the current pulses are supplied to the selected heating elements, thereby printing the dot pattern at high speed. In this case, the density of the picture element becomes low since the number of dots which constitute the dot pattern of one line is small.
Since the dimensions of the heating elements to be used in the thermal printers of the high density and high speed types are mutually different, in order to constitute the thermal printer which can selectively execute the high density and high speed printing operations, it is considered to be needed to use a special print head having two kinds of heating elements for use of, e.g., the high density and high speed printing operations.
Moreover, conventionally, there has been proposed such a thermal printer that can change the dot space in the printing direction or line direction by changing the rotating speed of a carriage drive motor in order to change the size of the character to be printed. However, in the thermal printer of this kind, an unnatural character pattern may be printed since only the transverse width of the character to be printed can be changed.